A conventional rib assembly 2 as shown in FIGS. 1-5 comprises: a top rib 21 having an inner end 211 pivotally secured to an upper notch 3 fixed on a top of a central shaft 1, a stretcher rib 22 having an inner end 221 pivotally secured to a lower runner 4 slidably held on the central shaft 1 with the runner 4 engageable on a spring catch 15 resiliently retained on the shaft 1 for positioning the rib assembly of the umbrella at an opening state as shown in FIG. 1, an intermediate rib 23 having a tail rib 26 pivotally connected to an outer end of the intermediate rib 23, an intermediate connecting rib 25 having its outer end pivotally connected with the intermediate rib 23 through a joint 24 fixed on an inner end of the rib 23 and having an inner end of the intermediate connecting rib 25 pivotally connected with an outer portion of the top rib 21, and an auxiliary folding spring 5 retained between the stretcher rib 22 and the intermediate rib 23 for helping folding the ribs of the rib assembly 2 when closing the umbrella.
The central shaft 1 includes: a lower tube 11 secured with a grip 12, a middle tube 13 telescopically engageable with the lower tube 11, and an upper tube 14 telescopically engageable with the middle rib 13.
The top rib 21 of such a conventional umbrella rib assembly has an outermost end 212 pivotally connected with a pair of lugs 220 by a pivot (rivet or eyelet) 220a. The lug 220 as fixed on the stretcher rib 22 is protruded above a side wall of the stretcher rib 22 to occupy a volume which will influence the folding volume when closing the umbrella.
The top rib 21 is formed with a U shaped cross section, having a pivot or rivet 213a transversely secured on an outer portion of the top rib 21 for pivotally connecting an inner end portion 251 of the intermediate connecting rib 25. Since the pivot 213a has an appreciable length and the width of the top rib 21 can not be greatly minimized in consideration of the mounting of the pivot 213a on the rib 21, the pivot 213a and the top rib 21 may thus be retarded against the side walls of the stretcher rib 22, and the top rib 21 can not be completely embedded into the U shaped groove as recessed in the stretcher rib 22 (FIGS. 4, 5), thereby being impossible to greatly minimize the folding volume of the rib assembly when closing the umbrella.
Each umbrella may be consisting of six or eight sets of rib assembly 2. The total volume of the closed umbrella by folding the rib assembly 2 is therefore unable to be greatly minimized.
The present inventor has found the drawbacks of the conventional rib assembly of the umbrella, and invented the present slim rib assembly for greatly minimizing the folding volume of the umbrella rib assembly, beneficial for making a mini pocketable folding umbrella.